1. Field of the Invention
The present invention is related to methods and compositions for safely modifying the burn rate of solid rocket propellants containing nitrocellulose (NC), without increasing the sensitivity of the propellant to shock detonation. More particularly, the present invention is related to a castable, double-base solid rocket propellant utilizing a ballistic modifier pasted in an inert polymer to modify the burn rate thereof.
2. Background Art
In the manufacture of solid rocket motors, a number of components are required. There must be an adequate rocket motor case. The rocket motor case is designed to form the exterior of the rocket motor and provides the essential structural integrity for the rocket motor. Conventionally, the rocket motor case is made from a rigid, yet durable, material such as steel or filament wound composite.
A solid rocket propellant is generally placed within the interior of the rocket motor case. The propellant forming the grain is conventionally burned within the interior of the rocket motor case. The formation of high pressure hot gases upon burning of the propellant, and the subsequent exit of those gases through the throat and nozzle of the case provide thrust to propel the rocket motor.
There are two major classes of propellants used in conventional applications. These include solid propellants and liquid propellants. Solid propellants have been developed as the preferred method of powering most missiles and rockets for military, commercial, and space applications. This disclosure specifically addresses solid rocket fuels.
A crucial consideration in solid propellants is providing a means for controlling the burn rate of the propellant. It is important that the propellant burn at a controlled and predictable rate without performance loss. Excessively high burning rate creates pressures within the casing that may exceed its design capability, resulting in damage or destruction to the device. Insufficient burn rate may not provide sufficient thrust to propel the rocket motor over the desired course. Accordingly, it is conventional in the art to add materials to the propellant to control the burn rate of the propellant. With control of the burn rate of the propellant, proper operation of the rocket motor or other similar device is possible.
Materials that control the burn rate are referred to as burn rate modifiers or ballistic modifiers. In order to achieve an acceptable burn rate, certain metals have been commonly added to the propellant as ballistic modifiers, but these metals have proven relatively toxic. For example, lead is the most widely used burn rate modifier for certain classes of solid propellants. Lead, however, is known to be a hazardous, toxic, and polluting metal. Concern with lead pollution in society as a whole is on the rise, and serious health problems are known to be associated with lead poisoning and lead pollution.
Carbon fibers have been used with acceptable effect to replace lead as a ballistic modifier, as in U.S. Pat. No. 5,372,664, to overcome the above-noted shortcomings of lead as a burn rate additive. However, the use of carbon fibers does not lower the burning rate enough for certain tactical applications.
Accordingly, it would be a significant advancement in the art to provide methods and compositions for modifying propellant burn rates that maintain a high level of insensitivity of the mixture to shock detonation, while minimizing the toxicity problems encountered with conventional burn rate modifiers. It would be a significant advancement in the art to provide propellant compositions of such properties that do not exhibit increased sensitivity, while still retaining high energy.
Generally, it is also necessary that the rocket motor perform with reduced or eliminated smoke output. As an example, in tactical rocket motors, the production of smoke may obscure the vision of pilots or drivers of a craft or vehicle firing the tactical rocket. In addition, the production of smoke makes tracking the source of the motor easier, which is a serious disadvantage during military operations. Therefore, it would be a significant advancement in the art to provide propellant compositions of such properties that do not exhibit increased sensitivity, while still retaining high energy, and performing with eliminated or reduced smoke output.